This invention relates to integrated circuit decoupling capacitors, such as decoupling capacitors for minimizing power supply noise.
Decoupling capacitors may be used to help power sources provide more stable power to powered circuit components. Decoupling capacitors allow high frequency noise on direct current (DC) power lines to be shunted directly between the lines, preventing the noise from reaching powered circuit components. If a power supply is required to switch between various modes of operation, an adequate decoupling capacitance can act as an energy reserve, lessening the magnitude of undesired dips in voltage during mode switching events.
Advances in integrated circuit design sometimes require power supplies to supply stable power for integrated circuits operating at high data rates and clock speeds. This requires increasing amounts of decoupling capacitance per integrated circuit area. A large decoupling capacitance could occupy a disproportionate amount of valuable surface area on an integrated circuit. An efficient and effective way is needed to implement large decoupling capacitances on an integrated circuit in order to maximize their effectiveness and minimize their footprint on the integrated circuit.
Decoupling capacitors for reducing power supply noise are sometimes placed adjacent to an integrated circuit on a printed circuit board. However, use of external decoupling capacitors arrangements such as these can introduce undesired interposed inductances and resistances, reducing the effectiveness of the decoupling capacitors in reducing power supply noise.
Conventional on-chip decoupling capacitors have been implemented using large, localized unitary gate oxide capacitor structures. While this type of arrangement may help to reduce power supply noise, large capacitor structures such as these are vulnerable to faults. If a fault shorts a large gate oxide capacitor, an unacceptably large current could flow across the shorted capacitor rendering the integrated circuit unusable. Such a fault could arise during production or in the field as a result of a latent dielectric defect. As larger and larger decoupling capacitances are implemented on integrated circuits to accommodate increasing data rates and power supply mode switching, the chances of experiencing this type of fault tends to increase. Moreover, decoupling capacitors that are localized in a particular portion of an integrated circuit tend not to be as effective as might be possible using other schemes.
It would therefore be desirable to provide improved integrated circuit decoupling capacitors.